The present invention relates to a synchronizer in a vehicle gearbox, comprising a guide sleeve intended to be non-rotatably joined to a shaft in the gearbox, an engaging sleeve which is non-rotatably, but axially displaceably, mounted on the guide sleeve, an engaging ring provided with exterior engaging teeth and which is intended to be solidly joined to a gear rotatably mounted on said shaft and is lockable relative to the guide sleeve by axial displacement of the engaging sleeve from a neutral position to an engagement position, in which interior engaging teeth on the engaging sleeve engage the exterior teeth on the engaging ring, and a synchronizing ring cooperating with the engaging sleeve and the engaging ring, said synchronizing ring having a conical frictional surface which is movable to engagement with a facing conical frictional surface on the engaging ring.